An electrophotographic reproduction system is used to transfer images onto paper or other medium. The electrophotographic reproduction system may be a copier, duplicator, printer, or the like. The images may be analog or digital. The electrophotographic reproduction system typically has a photoconductor, which may have a drum, belt, or other configuration. A belt-type photoconductor usually forms a continuous loop and is mounted on rollers for movement through the electrophotographic reproduction system. A drum-type photoconductor usually forms a cylindrical shape that is mounted on one or more rollers or another device to rotate on its axis in the electrophotographic reproduction system. A photoconductor typically has a photosensitive film layer covering an electrically conductive layer. There may be intermediate layers between the film and conductive layers. The photoconductor usually moves past or through a charging device, an exposure machine, a development station, a transfer mechanism, and a cleaning station. The electrophotographic reproduction system also may have a logic control unit (LCU) or other microprocessor, a graphic user interface, and other components.
As the photoconductor moves through the electrophotographic reproduction system, the charging device electrostatically charges a frame or portion of the photoconductor surface. The exposure machine optically exposes or projects an image onto the frame with the charged surface to form an electrostatic latent image on the photoconductor. The photoconductor moves the electrostatic latent image through the development station, which deposits toner onto the photoconductor. The toner is also is electrostatically charged and thus adheres to the oppositely-charged portions of the electrostatic latent image on the photoconductor. The photoconductor moves the resulting toner image through the transfer mechanism, where the toner image is transferred onto a sheet of paper or other medium. The paper subsequently passes through a fuser device prior to exiting the electrophotographic reproduction system. The fuser device affixes the toner to the sheet using elevated temperature and pressure. The photoconductor is refreshed at the cleaning station in preparation for the next image transfer. The cleaning station removes residual toner and electrostatic charges from the photoconductor.
Many electrophotographic reproduction systems use a corona charger to electrostatically charge the surface of the photoconductor. A corona charger usually has one or more wires positioned in a housing adjacent to the photoconductor. Each wire is held under tension by support members. Multiple wires usually are positioned parallel to each other on separate support members. When a high voltage potential is applied to the wires, a corona or ion field is generated around the wires. The corona causes current to flow to the photoconductor, thus depositing an electrostatic charge on the surface of the photoconductor. The wires may be configured and positioned to deposit a substantially uniform charge on the photoconductor.
The corona charger typically is integrated within a charger assembly for the electrophotographic reproduction system. The charger assembly usually includes other components for operation of the corona charger such as electrical circuitry, controls, and the like. The corona charger also may have a shield, a ground plane, and a grid electrode. The shield partially surrounds the wires without obstructing the area between the wires and the photoconductor. The shield usually is made of an electrically insulative material. The ground plane typically is positioned on the side of the wires that is opposite the photoconductor. The ground plane usually is made of an electrically conductive material. The ground plane may have an applied electrical bias or may be grounded. The grid electrode is positioned between the wires and the photoconductor. The grid electrode may be a conductive plate or sheet with slits or holes such as a mesh, a screen, or the like. The grid electrode also may be a plurality or network of wires. A bias voltage usually is applied to the grid electrode. The bias voltage creates an electric field to control the current flow between the wires and the photoconductor.
With repeated operation of the electrophotographic reproduction system, the wires in the corona charger may deteriorate and may become contaminated. The deterioration and contamination may increase the non-uniformity of the electrostatic charge on the photoconductor beyond acceptable levels for image quality. The deterioration and contamination also may affect the voltage applied to the wires. In addition, the deterioration and contamination may cause corona discharges.
The wires in a corona charger usually are replaced on a frequent basis to avoid or address the affects of deterioration and/or contamination. For some electrophotographic reproduction systems, the charger assembly is discarded and a new charger assembly installed when the wires become or are near to becoming deteriorated or contaminated. The installation of a new charger assembly may increase operating costs, especially in larger or more sophisticated electrophotographic reproduction systems. Operators also may delay the installation of the new charger assembly to avoid the expense. This delay may cause additional maintenance, reduce system durability, and affect image quality.
For other electrophotographic reproduction systems, the individual wires in the corona charger are replaced when the wires become or are near to becoming deteriorated or contaminated. Wire replacement typically is time consuming and results in longer downtime for the electrophotographic reproduction system. Wire replacement usually is done better by a service technician or someone with like experience and/or training. Each wire is physically handled. The old wires are removed from the support members. The new wires are attached to the support members. The new wires may attract contaminants from an installer's hands. In addition, the tension in each wire must be accurately set. The tension controls the vibration frequency of the wires. A change in the vibration frequency may affect image quality and may cause electrical discharges form the corona charger. If there is insufficient tension, the wire may sag and come close enough to cause an electrical discharge to the photoconductor or other components in the electrophotographic reproduction system. If there is too much tension, the wire may break when installed or during later operation of the electrophotographic reproduction system. After the new wires are installed on the support members, the corona charger may need to be installed and aligned properly with the photoconductor. The charger assembly may require additional adjustments.